PC not starting; Memory fault?

PC refused to start after working OK for over a year.Single repeated beep from unit. Internet search suggested memory problem.Removed & refitted both sticks of 256Mb PC2700 DD333 memory. No better. Remove one stick only & PC works fine! It doesn't matter which stick I fit or in which slot,PC works ok.If I fit both back together PC refuses to play! Does this mean one memory module has a fault & they are not compatible together or is it more likely a motherboard fault?(or something else entirely!)I would happily upgrade memory if I thought this was the answer.

if you remove a stick and it works, it has to be the memory. Strange how they work independantly but not together, but it could be one has developed a timing problem. This means they will work seperate but not together.

I would change them both, but get a decent make of memory. There are cheap ones out there which are nasty, and to be on the safe side get it all in 1 stick this time.

run it with each stick in turn then both together. I had the same problem recently. It was caused by having 2 rams of different makes getting out of sync on memory intensive programs. Each worked fine on their own but together there was a conflict.